Ukraine and Nuclear Proliferation

Russia's invasion has made U.S. assurances seem meaningless.

Updated March 19, 2014 9:00 p.m. ET

The damage to world order from Vladimir Putin's invasion of Crimea will echo for years, but one of the biggest casualties deserves more attention: the cause of nuclear nonproliferation. One lesson to the world of Russia's cost-free carve-up of Ukraine is that nations that abandon their nuclear arsenals do so at their own peril.

This story goes back to the end of the Cold War and the collapse of the Soviet Union. Russia's nuclear arsenal was spread among the former Soviet republics that had become independent nations....